Documentation sections

RF Attenuator Designer

POSThttps://rftools.io/api/py/v1/calculate

Slug attenuator-designer. Design Pi and T attenuator pads with exact resistor values and nearest E24 matches. Enter attenuation and impedance for both topologies. Free, instant results.

Inputs

Send every one of these in inputs, in the units shown. Most are required: a call without one is refused (400) and costs nothing; one the calculator can do without takes the default shown. An input outside its range is still computed and flagged in the provenance.

Inputs of attenuator-designer
Name	Unit	Range	Default	Description
attenuationnumber	dB	0.1 … 40	6	Desired attenuation in dB
impedancenumber	Ω	1 … 1000	50	Source and load impedance (must be equal for a matched pad)
eSeriesnumber	none	0 … 96	24	Rounds every part to the nearest value in the series; the response and the export are the rounded design's.One of: 0 Ideal values · 12 E12 (10%) · 24 E24 (5%) · 48 E48 (2%) · 96 E96 (1%)

Outputs

Returned in values, by key. A value that is unbounded or undefined is null.

Outputs of attenuator-designer
Field	Unit	Description
piR1headline	Ω	Pi topology: two equal shunt resistors (exact value)
piR1Nearest	Ω	Pi topology: the shunt resistors rounded to the part series (E24 by default; the exact value with ideal values)
piR2	Ω	Pi topology: series resistor (exact value)
piR2Nearest	Ω	Pi topology: the series resistor rounded to the part series (E24 by default; the exact value with ideal values)
tR1	Ω	T topology: two equal series resistors (exact value)
tR1Nearest	Ω	T topology: the series resistors rounded to the part series (E24 by default; the exact value with ideal values)
tR2	Ω	T topology: shunt resistor (exact value)
tR2Nearest	Ω	T topology: the shunt resistor rounded to the part series (E24 by default; the exact value with ideal values)
piAttenuationBuilt	dB	The attenuation of the Pi pad the rounded resistors build, between Z₀ at its input and Z₀ at its output (the transducer loss of shunt R1, series R2, shunt R1)
piInputImpedanceBuilt	Ω	The impedance the rounded Pi pad presents at its input with Z₀ on its output, R1 ∥ (R2 + R1 ∥ Z₀); Z₀ with ideal values

Calling it

Calculate: one call, the request and response in full, and its errors.
Batch: this calculator with others, or a sweep, in one request.
Solve for a target: the value of one input that brings an output to a target.

curl -X POST https://rftools.io/api/py/v1/calculate \
  -H "X-API-Key: $RFTOOLS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "slug": "attenuator-designer",
    "inputs": {
      "attenuation": 6,
      "impedance": 50,
      "eSeries": 24
    }
  }'

import rftools

client = rftools.Client()  # reads RFTOOLS_API_KEY, or the key `rftools login` saved

result = client.calculate("attenuator-designer", {"attenuation": 6, "impedance": 50, "eSeries": 24})
print(result.values)
print(result.warnings, result.provenance.formula_ref)

const response = await fetch("https://rftools.io/api/py/v1/calculate", {
  method: "POST",
  headers: {
    "X-API-Key": process.env.RFTOOLS_API_KEY,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "slug": "attenuator-designer",
    "inputs": {
      "attenuation": 6,
      "impedance": 50,
      "eSeries": 24
    }
  }),
});
console.log(response.status, await response.json());

package main

import (
	"bytes"
	"fmt"
	"io"
	"net/http"
	"os"
)

func main() {
	body := []byte(`{
	  "slug": "attenuator-designer",
	  "inputs": {
	    "attenuation": 6,
	    "impedance": 50,
	    "eSeries": 24
	  }
	}`)
	req, err := http.NewRequest("POST", "https://rftools.io/api/py/v1/calculate", bytes.NewReader(body))
	if err != nil {
		panic(err)
	}
	req.Header.Set("X-API-Key", os.Getenv("RFTOOLS_API_KEY"))
	req.Header.Set("Content-Type", "application/json")
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()
	out, _ := io.ReadAll(res.Body)
	fmt.Println(res.Status, string(out))
}

application/json

{
  "slug": "attenuator-designer",
  "values": {
    "piR1": 150.47602375372455,
    "piR2": 37.35187703354018,
    "piR1Nearest": 150,
    "piR2Nearest": 36,
    "tR1": 16.613942458312202,
    "tR2": 66.93104064770615,
    "tR1Nearest": 16,
    "tR2Nearest": 68,
    "piAttenuationBuilt": 5.904009040065147,
    "piInputImpedanceBuilt": 49.328859060402685
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:attenuator-designer",
    "version": "api@3f2c1a9b04de",
    "formulaRef": "Vizmuller, \"RF Design Guide\" (1995); Matthaei et al. (1964)",
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "attenuation": {
          "min": 0.1,
          "max": 40,
          "unit": "dB"
        },
        "impedance": {
          "min": 1,
          "max": 1000,
          "unit": "Ω"
        },
        "eSeries": {
          "min": 0,
          "max": 96,
          "unit": ""
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "attenuation": 6,
      "impedance": 50,
      "eSeries": 24
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "attenuation"
      ],
      "msg": "Input should be a valid number, unable to parse string as a number",
      "input": "abc"
    }
  ]
}

An input sent as text. Nothing was counted.

{
  "detail": "More than 120 requests in 60 seconds from this address.",
  "errorKind": "rate_limited",
  "limit": 120,
  "windowSeconds": 60,
  "upgradeUrl": "https://rftools.io/pricing/"
}

Too many requests in a minute, with Retry-After.

Same inputs on the calculator pageRF Attenuator Designer, at these values